Using similar tactics as regularly employed by Apple, Facebook's invite offers just a cryptic one line message, asking journalists to "come and see what we're building".

There has been persistent speculation that Facebook is working on its own smartphone as a way to gain greater control over the hardware and software ecosystem.

Reports emerged last year that Facebook was collaborating with Taiwanese smartphone maker HTC on a mystery project codenamed 'Buffy'. Other reports have said that the firm poached engineers from Apple's iPhone team to work on the venture.

Facebook and HTC previously collaborated on the ChaCha and Salsa smartphones, which boasted deep integration of the social network and dedicated Facebook buttons on them. But many people believe that the obvious next step for Facebook would be creating its own fully branded handset.

Facebook is available on most smartphone and tablet platforms, with the social network's mobile user base growing by 67% over the last year. Around 600m users log on to their Facebook profile every month using a mobile device.

Facebook is one of the most popular apps on the market, but the company is just one of many services vying for customers' attention.

Creating a Facebook phone would allow the company to more closely integrate its social network, messenger and photo services, such as the newly-acquired Instagram, into the branded handset, giving it much more control of the communications ecosystem.

The firm has a multi-billion dollar war chest from its blockbuster initial public offering last year and so is able to acquire and source some of the best expertise in the world for the venture.

It has also seen Google, a major rival in the online advertising market, recently make big strides into the hardware market with the $12.5bn purchase of Motorola Mobility, maker of smartphones and tablets.

In a sense, Facebook knows that it must move beyond just online ads over Facebook.com and its mobile apps to generate the type of revenues that Google enjoys. A Facebook phone with a proprietary operating system could be a good start to please those edgy investors.

He said that this is because it would not significantly increase the Facebook user base.

"If we make a phone we could get maybe ten million users? Twelve million users? That doesn't move the needle for us," he said.

"Building a phone is the wrong strategy for us."

However, earlier in the year he hinted that Facebook's ambitions do go beyond just creating apps and services.

"We want not just to have apps that people use, but be as deeply integrated as possible, where other apps can build on top of Facebook," he said in response to a question about Facebook on mobile during a call with analysts.

We will find out on January 15 whether Facebook does intend to launch its own smartphone, or has something else up its sleeve. Digital Spy Tech will be at the London leg of launch event, so stay tuned for our live coverage next week.

In the mean time, would you want or buy a Facebook phone? Let us know below...